1. Field of the Invention
The present invention relates generally to an exhaust gas recirculation (EGR) control system for an internal combustion engine equipped with an electronically controlled fuel injection device and particularly to an EGR control system for an internal combustion engine lacking an intake passageway provided with a venturi in which system it is impossible to employ the so-called venturi vacuum for operating a diaphragm unit of an EGR control valve so that the EGR control valve controls the EGR amount in accordance with the flow rate of engine taken air.
2. Description of the Prior Art
As is well known in the art, an internal combustion engine is provided with an exhaust gas recirculation (EGR) control system for reducing the maximum temperature of combustion in the engine to reduce the production of nitrogen oxides (NOx) of noxious emissions of the engine by recirculating exhaust gases of the engine into air taken thereinto. When the EGR amount of engine exhaust gases thus recirculated is increased, since on the one hand although the effect of reducing the production of nitrogen oxides is increased, on the other hand a bad influence exerted on the operational performance of the engine is increased, it is necessary to control the EGR amount to maintain the EGR rate of the EGR amount to the amount of engine taken air at a desired constant value in all operating ranges of the engine as a rule.
For this purpose, in an internal combustion engine including an intake passageway provided therein with a carburetor venturi, an EGR control valve for controlling the EGR amount is operated by operating a diaphragm unit in accordance with a vacuum in the venturi which is highly reliable as a function of the flow rate of engine taken air or in accordance with an amplified venturi vacuum.
However, since an internal combustion engine equipped with an electronically controlled fuel injection device includes no intake passageway provided therein with a venturi, it is impossible to employ a venturi vacuum for operating a diaphragm unit of an EGR control valve. In this instance, it is undesirable to provide a venturi in the intake passageway of the engine of this type as a solution to this problem. This is because the provision of a venturi in the intake passageway nullifies an advantage of the engine that the resistance to the flow of air taken into the engine is small so that the engine is superior in operational performance owing to no provision of a venturi in the intake passageway.